Method of producing gasoline from cracked distillate



Patented den. 7,. I93 I STATS,

GEORGE 1?. KOCH, OIF MARTINEZ, CALIFORNIA, ASSIGNO R TO SHELL OIL COMPANY, OF

, SAN FRANCISCO, CALIFORNIA, A CORPORATION 01E CALIFORNIA METHOD OIE,. I ERODUCING GASOLINE FROM CRACKED DIS'IILLATE No Drawing.

My invention relates to the refining of petroleum products and particularly to the refining of cracked distillates.

It is common practice to subject petroleum oils to heat and pressure for the purpose. of

, changing their physical characteristics, this practice being known as cracking, and the.

distillates resulting from the cracking operation being known as cracked distillates. I

The amount of such cracked distillate now produced is very large, such distillate beingusually a gasoline or a distillate which can be redistilled to produce a large proportion ofgasoline. p I

, Cracked distillates, due to the process by which theyoa're produced, contain considerable quantities of unsaturated hydrocarbons and often contain unstable compounds and sulfur compounds such as mercaptans, sulfides, 'disulfides and polysulfides. These compounds give a poor color and odor .to

the distillate as initially produced and both the color and odor get worse-as the distillate stands. For the purpose of im proving the color andodor and the keeping qualities of the final products, such as gasoline, produced. from such cracked dishydrocarbons form a very desirable component of'gasoline designed to be used as motor fuel, it is highly desirable that they be conserved. 7

It is an object of my invention to provide methods by which unstable and undesirable compoundsmay be removed from cracked I distillates without unfavorably affecting the useful unsaturated hydrocarbons or the dis tillates themselves.

The objectionable compounds, including sulfur compounds, found in cracked distillates cannot be readily separated from the useful saturated and unsaturated hydrocar- Application filed. March 29,1926. Serial No. 98,364.

bons by physical methods of refining like distillation or extraction with various solvents,

- for the reason that they have physical characteristios similar to those'ofthe saturated and desirable unsaturated hydrocarbons in respect to boiling points and solubility in various liquids.

I have discovered that a good separation of the undesirable compounds from the valuable distillates and unsaturated hydrocarbons can be accomplished by treating a cracked distillate with nitric acid which, if'

the proper proportions arev used, acts upon the undesirable compounds without materially affecting the valuable hydrocarbons. It is well knownthat nitric acid'is a powerful oxidizing-agent and it would be expected that its use in concentrated form would result in a marked action on substances like the unsaturated hydrocarbonswhich have a decided affinity for oxygen. I have found, however, that the nitric acid has apparently a marked preference for the undesirable compounds, particularly those containing sulfur, and when-properly used, does not materially attack or affect the useful hydrocarbons. I appreciate that this is not only an unexpected result but'one which iscontrary to present accepted chemical practices and teaching, but I have practiced the invention on a large scale and the results given herein are those obtained in actual practice.

In using my invention I first treat the cracked distillate with concentrated nitric acid. I then .wash the distillate with waterg. treat it with strong alkali such as 'sod'um hydroxide or potassium hydroxide; again wash itwith .water; treat it with sulfuric acid; Wasln neutralize with soda and again wash with water. i

The treatment with alkali and sulfuric acid is that previously used in the art, for the refining of similar distillates except that since the nitric acid combines with theil'ntlesirable' compounds, the amount of sulfuric acid to be used can be reduced considerably'.';; b

I find that in refining distillatesfcontaining about 1.0 per cent of sulfur, irrespective of the chemical combination in which the element may be, about 1.0 per cent of concentrated nitric acid should be used, the proportion of nitric acid varying with the proportion of sulfur inxthe distillate to be treated.

The sulfur in the distillate is originally in such a form that it distils over with the gasoline vapors. For example, in distilling gasoline from a cracked distillate containing about 1.0 per cent of sulfur as determined by quantitative analysis, I found that in the per cent distilled off I obtained .87 per cent of sulfur. cracked distillate to the above nitric acid treatment, I reduced the proportion of sulfur in the first 50 per cent of gasoline distilled to 0.11 per cent. q

The above mentioned original cracked distillate contained initially about 25 per cent of unsaturated hydrocarbons which, being quite volatile, form a most desirable component of gasoline. I found after treating such distillate for one hour with 1.0 per cent of concentrated nitric acid, that there was no reduction in the proportion of unsaturated hydrocarbons and practically no sludge formation.

I found further, if the same distillate were treated as above described by alkali and acids with intermediate washings but entirely omitting the step of using nitric acid, that while .some reduction in the sulfur content was observed, it was much less than where nitric acid was used, and that if the alkali and sulfuric acid treatments were carried to a point where the undesirable compounds were eliminated there was a considerable destruction of unsaturated hydrocarbons, a considerable formation of acidsludge, and considerable loss in value of product.

The chemistry of the undesirable com them and producing reaction products which,

as they have a much higher boiling point than the distillate, can be separated therefrom by distillation; or reaction products which being wate'rsoluble are washedout by the washing treatment or perhaps reaction products which yield readily to the later alkali or acid treatment to form substances which are readily separable from the distillate.

trated nitric acid'in equal proportion by By subjecting the original.

comprises: determining the proportion of the sulfur in the distillate to be treated; treating said oils in liquid phase with concentrated nitric acid in equal proportion by weight to that of the sulfur content of the distillate, irrespective of the form of combination of the element, Without materially affecting the unsaturated hydrocarbons; and thereafter washing the oil with water, alkali and acid to re move the reaction products formed by the union of said nitric acid with said compounds.

-3. A method of separating undesirable sulfur compounds from distillates consisting of substantially only the gasoline fractions of petroleum oils containing unsaturated hydrocarbons, which comprises: treating said oils in liquid phase with nitric acid in substantially equal proportion by weight to that of the sulfur to be removed, irrespective of the form of combination of the element, without materially affecting the unsaturated hydrocarbons; and thereafter removing the reaction products formed by the union of said nitric acid'with said compounds.

4. A method of separating undesirable sulfur compounds from distillates consisting of substantially only the gasoline fractions of petroleum oils containing unsaturated hydrocarbons, which comprises: treating said oils in liquid phase with nitric acid in substantially equal proportion by weight to that of the .sulfur to be removed, irrespective of the form of combination of the element, without materially affecting the unsaturated hydrocarbons; and thereafter distilling off the oil and unsaturated hydrocarbons from the reaction products formed by the union of said nitric acid with said compounds.

5. A method of separating undesirable sulfur compounds from distillates consisting of substantially only the gasoline fractions of petroleum oils containing unsaturated hydrocarbons, which comprises: treating said oils in liquid phase with nitric acid in substan tially equal proportion by weight to that of the sulfur to be removed, irrespective of the form of combination of the element, without materially affecting the unsaturated hydrocarbons; and thereafter washing the oil with water to remove the reaction products formed by the union of said nitric acid with said compounds.

6. A method of separating undesirable sulfur compounds from distillates consistingof substantially only thegasoline fractions of petroleum oils containing unsaturated hydrocarbons, Which comprises: treatingsaid oils in liquid phase with nitric acid in substantially equal proportion by Weight to that of the sulfur to be removed, irrespective of the form of combination of the element, Without materially affecting the unsaturated hydrocarbons; and thereafter washing the oil with water, alkali and acid to remove the reaction products formed by the union of said'nitric acid with said compounds. i

7. A method of producing a gasoline of good color and odorfrom a cracked distillate containing objectionable sulfur compounds and desirable unsaturated hydrocarbons,

which comprises: treating the cracked distilby weight to the amount of the sulfur content of the oil, irrespective of the: form of combination of the element, without mate-.

. rially affecting the unsaturated hydrocarbons; washing the distillate with water to remove a portion of the reaction productsformed by the union of said nitric acid with said compounds; and thereafter'distilling 01f gasolineand unsaturated hydrocarbons from said distillates.

9. A method of producing a gasoline of good color and odor from a cracked distillate containing objectionable sulfur comounds and desirable unsaturated hydrocarons, which comprises: treating the cracked distillate in liquid phase with concentrated nitric acid in an amount substantially equal byweight to the amount of the sulfur content of the oil, irrespective of the form of combination of the element, Without materially affecting the unsaturated hydrocarbons; subj ecting the above treated distillate to further alkali and acid action and washing; and thereafter distilling off gasoline and unsaturated hydrocarbons from said distillates.

10. A method of-producing a gasoline of good color and odor from a cracked distillate containing objectionable sulfur compounds and desirable unsaturated hydrocarbons, which comprises: treating the cracked distillate in liquid phase with concentrated nitric acid in an amount substantially equal by weight to the amount of the sulfur content of the oil, irrespective of the form of 001m bination of the element, without materially affecting the unsaturated hydrocarbons; washing the distillate With water to remove a portion of the reaction products formed by the unionof said nitric acid with said compounds; subjecting the distillate to further alkali. and acid action and Washing and thereafter distilling off gasoline and unsaturated hydrocarbons from said distillates.

In testimony whereof, I have hereunto set my hand at Martinez, California, this 12 day of March, 1926.

GEORGE P. KOCH. 

